Reinforced Bias- Or Radial-Carcass Tire

ABSTRACT

The invention relates to a tire having at least one carcass reinforcement comprising reinforcers, surmounted radially on the outside by a crown reinforcement, itself radially on the inside of a tread, said crown reinforcement being made up of at least one layer of reinforcement elements, said tread being connected to two beads by way of two sidewalls, said beads being intended to come into contact with a rim flange having a rim flange top C, each bead having at least one circumferential reinforcement element, said carcass reinforcement comprising an end at each bead, the end of the carcass reinforcement being turned up once in an outward radial direction of the tire and about said bead wire, so as to form a turnup, then being folded in said radially inward direction so as to form a fold forming a radially external end and three adjacent parts along an axial axis made up of a central part, of an axially internal lateral part, and of an axially external lateral part. 
     The tire is characterized in that the radially external end of the turnup is disposed between the rim flange top C and a point D, said points C and D being situated at the surface of the sidewall and disposed on either side of a point E situated on the sidewall corresponding to the nominal section width, said point D being disposed at a maximum radial length equal to 85% of the length present between the axial end S of the crown reinforcement and the rim flange top C.

The invention relates to cross-ply or radial tires.

Radial tires are gradually being imposed on various markets, notably themarket for passenger vehicle tires. This success is due in particular tothe endurance, comfort and low rolling resistance qualities that radialtires have to offer.

The main parts of a tire are the tread, the sidewalls and the beads. Thebeads are intended to come into contact with the rim. In a radial tire,each of the main parts of which the tire is made, namely the tread, thesidewalls and the beads, has functions that are clearly separated fromone another, and therefore has a well-known specific makeup.

A radial tire is essentially reinforced by a carcass reinforcementcomprising at least one carcass ply set at an angle substantially equalto 90° with respect to the circumferential direction of the tire. Thiscarcass reinforcement is surmounted radially on the outside, and underthe tread, by reinforcing plies that form a belt.

A cross-ply tire differs from a radial tire in that there are at leasttwo crossed plies set at angles other than 90° with respect to thecircumferential direction of the tire. The plies are said to be“crossed” because the angles are of opposite sign from one ply to thenext.

It will be recalled that the circumferential direction of the tire isthe direction in a plane perpendicular to the rotation axis of the tireand tangential to the tire belt reinforcement.

Since the emergence of radial tires, certain cross ply tires have alsobeen provided with a belt reinforcement under the tread.

In both these types of tire, the tread, in direct contact with theground, notably has the function of providing contact with the roadwayand needs to adapt to the shape of the ground. The sidewalls for theirpart absorb the unevennesses of the ground by transmitting themechanical forces required to support the load of the vehicle and allowit to move.

The belt reinforcement is a reinforcement which, on the one hand, needsto be sufficiently rigid with regard to edge deformations so that thetire can develop the cornering thrust necessary for steering, andtransmit torque for traction or for braking and, on the other hand, bevery soft in bending, that is to say allow variations in curvature inits plane in order to provide a sufficient area of contact of the tirewith the ground.

As a result, the belt reinforcement generally has a composite structureallowing it to offer the required rigidity for a relatively low weight.The belt reinforcement is generally made up of at least two plies set atdifferent angles, comprising reinforcers in the form of cords, coatedwith elastomer composition. The reinforcer elements are crossed from oneply to the other with respect to the circumferential direction and mayor may not be symmetrical with respect to this direction.

Definitions:

-   -   “longitudinal direction” is the direction of running of the        tire,    -   “radial direction” is a direction that intersects the rotation        axis of the tire and is perpendicular thereto,    -   “axial direction” is a direction parallel to the rotation axis        of the tire,    -   “radially on the inside of” means closer to the rotation axis on        a straight line perpendicular to the rotation axis of the tire,    -   “radially on the outside of” means further away from the        rotation axis on a straight line perpendicular to the rotation        axis of the tire,    -   “equatorial plane or midplane” means a plane perpendicular to        the rotation axis of the tire and which divides the tire into        two substantially equal halves,    -   “transverse or axial direction of the tire” means a direction        parallel to the rotation axis,    -   “radial or meridian plane” means a plane which contains the        rotation axis of the tire.

Tires for heavy vehicles comprising a carcass ply provided with metalreinforcers, the final part of which at each bead is folded on itself,twice, in the radial direction towards the circumferential reinforcementelement, also known as bead wire, are already known from the documentJP2293207 A. According to that document, this final part is folded amidtwo layers of rubber.

The document EP 1,080,948A1 describes a tire comprising a carcassreinforcement turned up about a bead wire and then folded in an outwardaxial direction. This fold is coated with an elastomer compositioncomprising reinforcers.

Thus, there remains a need to be able to have a tire that has bettercornering thrust, which comprises fewer raw materials, and notably fewerlayers of elastomer, without impairing rolling resistance.

The subject of the invention is thus a tire having at least one carcassreinforcement comprising reinforcers, surmounted radially on the outsideby a crown reinforcement, itself radially on the inside of a tread, saidcrown reinforcement being made up of at least one layer of reinforcementelements, said tread being connected to two beads by way of twosidewalls, said beads being intended to come into contact with a rimflange having a rim flange top C, each bead having at least onecircumferential reinforcement element, said carcass reinforcementcomprising an end at each bead, the end of the carcass reinforcementbeing turned up once in an outward radial direction of the tire andabout said bead wire, so as to form a turnup, then being folded in saidradially inward direction so as to form a fold forming a radiallyexternal end and three adjacent parts along an axial axis made up of acentral part, of an axially internal lateral part, and of an axiallyexternal lateral part.

The tire is characterized in that the radially external end of theturnup is disposed between the rim flange top C and a point D, saidpoints C and D being situated at the surface of the sidewall, anddisposed on either side of a point E situated on the sidewallcorresponding to the nominal section width, said point D being disposedat a maximum radial length equal to 85% of the length present betweenthe axial end S of the crown reinforcement and the rim flange top C.

The tire according to the invention has the advantage of having a simpleand rapid design.

Preferably, the decoupling elastomer composition is present between theradially external end of said turnup and a point G situated radially onthe inside with respect to said end and at a distance from said radiallyexternal end by a length less than or equal to 10 mm

Between the points C and D, the reinforcers of the carcass ply may beset at an angle of less than or equal to 85° with respect to thecircumferential direction, and preferably equal to +75° or −75° withrespect to the circumferential direction.

The angle between each of the (central) and (lateral) parts of thecarcass ply follows the rules of the following shaping law, according towhich the angle of said parts evolves with the radius of the tire:

cos(α₁)=t×cos(α₀) where t=R₁/(R₀×(1+e))

where

-   -   α₀ is the initial angle before shaping    -   α₁ is the final angle after shaping    -   R₀ is the laying radius before shaping    -   R₁ is the laying radius after shaping    -   e is equal to 0.03 regardless of the type of tire

When applying this law, between the points C and D, and when the fold ismade towards the inward direction in the axial direction, thereinforcers of the carcass ply may be set at an angle successively equalto −75°, +75°, +75° starting from the most outward direction to the mostinward direction in the axial direction.

Between the points D and S, the reinforcers of the carcass ply may beset at an angle of greater than or equal to 85°, and preferably equal to90° with respect to the circumferential direction. The point Scorresponds to the axial end of the crown region.

Starting from the point S and in the direction of the axis ZZ′, thereinforcers of the carcass ply may be set at an angle equal to 90° withrespect to the circumferential direction.

The reinforcers of the carcass ply are preferably made of a textilematerial chosen from rayon, nylon, polyester, aramid or a mixturethereof.

Some of the reinforcers of the outer part of the carcuss ply may besectioned in the case of an inward turnup. Some of the reinforcers ofthe central part of the carcass ply may be sectioned in the case of anoutward turnup. This part may have between 3 and 8% of the reinforcersof the central part.

The reinforcers are cut at the end of the butting step during the methodfor manufacturing the tire so as to encourage the carrying out of thebutting step. The cut reinforcers are disposed in a limited and narrowregion, they are not scattered but concentrated in this region.

According to the invention, the crown reinforcement comprises at leastone ply radially on the outside of the carcass ply and radially on theinside of a tread.

According to the invention, no elastomer composition is present betweenthe central part and the axially external lateral part of the turnup.

The invention will now be described with the aid of examples anddrawings which follow and which are given purely by way of illustration,and in which:

FIG. 1 schematically shows the cross section of a half tire according tothe invention in a radial plane, according to a first embodiment;

FIG. 2 schematically shows an enlarged view in cross section of theradially lower part of a turnup, of the carcass ply, situated in what isknown as the bottom region of the tire, according to the same embodimentof the invention as the one shown in FIG. 1;

FIG. 3 schematically shows an enlarged view in cross section of theradially lower part of a turnup of the carcass ply, situated in what isknown as the bottom region of the tire, according to another embodiment;

In the various figures, identical or similar technical elements havebeen given the same reference numbers. In order not to overburden thetext, their descriptions are not repeated.

As FIGS. 1 and 2 show, the tire according to the invention, having theoverall reference 1, comprises at least one carcass reinforcement 2comprising reinforcers (not shown). A crown reinforcement S3 comprisingat least one layer of reinforcement elements (not shown) is surmountedradially on the inside of the carcass ply 2, followed by a tread 4radially on the outside.

The tread 4 is connected to two beads 5 by way of two sidewalls 6. Eachbead 5 comprises a circumferential reinforcement element 7, also knownas a bead wire. Each bead 5 is fitted into a rim flange 13 comprising arim flange top C

The carcass ply 2 comprises, at each bead 5, a final end 8 that isfolded on itself twice in the radial direction and in the inwarddirection with respect to the centre of the tire in the axial direction,in the direction of the circumferential reinforcement element 7. Thisfold makes it possible to bring said final end 8 close to thereinforcement element 7.

Thus, at the sidewalls 6, the carcass ply 2 comprises a turnup 12, andthree adjacent parts made up of a central part 10, an axially outerlateral part 9 and an axially inner lateral part 11.

Note that the nominal section width is the section width of a tiremounted on a rim and inflated; the section width being the distancebetween the two axially outermost points of the tire mounted on the rimand inflated.

Thus, the radially upper end 12 a of the turnup 12 can be disposed onthe surface of the sidewall between a point C and a point D.

According to the depiction in FIG. 1, the three adjacent parts 9, 10 and11 of the turnup of the carcass ply 2 are folded on themselves such thatthe central part 10 is adjacent to the lateral parts 9 and 11. Adecoupling elastomer composition 14 is disposed between the lateral part11 and the wall of the sidewall 2. This 14 is present as far as a pointF, situated on the sidewall, and at a distance equal to 17 mm from theupper part 12 a of said turnup 12 towards the inner part of the radialdirection. This composition 14 may also be present along a length equalto 60 mm from the upper part 12 a of the turnup towards the upper partof the radial direction. This composition 14 may be extended as far as aposition axially inside the point S.

The presence of such an elastomer composition makes it possible toprecisely adjust the behaviour and endurance of the tire.

In this particular embodiment, the reinforcers (not shown) of thecarcass ply 2 are set at an angle equal to 75° with respect to thecircumferential direction, between the points C and D, thereby making itpossible to maintain a correct cornering thrust.

These same reinforcers are set at an angle equal to 85° with respect tothe circumferential direction between the points D and S, thereby makingit possible to maintain good rolling resistance, and at an angle equalto 90° with respect to the circumferential direction in the regionradially inside the crown reinforcement 3.

In FIG. 3, it is possible to see that the end 8 of the carcass ply 2 isalso folded twice in the direction identical to that in FIG. 1. Thedepiction of this embodiment differs from that in FIG. 1 in that thedecoupling composition 14 is also present outside the axially outermostpart 9 of the turnup 12 as far as a point G situated on the carcass plyradially inside the end 12 a, and at a distance, by a length equal to 17mm, from said upper part 12 a of the turnup 12 towards the inner part inthe radial direction.

According to the invention, the absolute value of the angle of each ofthe three parts of the carcass ply is identical; only the sign of theangle of the axially outer part 9 changes with respect to the centralpart 10 and the axially inner part 11.

In the embodiment in FIGS. 2 and 3, the reinforcers (not shown) of thecarcass ply 2 are set at angles, with respect to the circumferentialdirection, that are identical to the embodiment in FIG. 1.

EXAMPLE 1 Cornering Stiffness

The measurements of cornering stiffness are obtained using a machineequipped with a rolling road and with a device for measuring thetransverse forces applied to the tire, depending on the load.

These measurements are carried out on a tire with the reference 205/55 R16 mounted on a rim 6.5 J 16, inflated to a pressure of 2.5 bar, andsubjected to a load of 483 daN. The tire is subjected to a speed of 80km/h with a cornering angle of +/−1 degree.

The results are set out in Table I below:

Tire according to the Control tire invention Cornering stiffness 100 106

As the table shows, the tire according to the invention improves thecornering stiffness by 6%.

EXAMPLE 2 Mass of the Tire

A measurement of the mass of the tire according to the inventioncompared with a control tire, for a reference 205/55 R 16, shows areduction in the overall mass of the tire of 3%.

1. Tire having at least one carcass reinforcement comprisingreinforcers, surmounted radially on the outside by a crownreinforcement, itself radially on the inside of a tread, said crownreinforcement being made up of at least one layer of reinforcementelements, said tread being connected to two beads by way of twosidewalls, said beads being adapted to come into contact with a rimflange having a rim flange top (C), each bead having at least onecircumferential reinforcement element, said carcass reinforcementcomprising an end at each bead the end of the carcass reinforcementbeing turned up once in an outward radial direction of the tire andabout said bead wire, so as to form a turnup, then being folded in saidradially inward direction so as to form a fold forming a radiallyexternal end and three adjacent parts along an axial axis made up of acentral part, of an axially internal lateral part, and of an axiallyexternal lateral part wherein a decoupling elastomer composition havinga secant modulus at 10% extension of greater than or equal to 10 MPa andpreferably greater than or equal to 30 MPa and less than or equal to 60MPa is present: between the axially internal lateral part and thecentral part of said turnup, and at the radially external end of saidturnup, said elastomer composition being present along a radial lengthcomprised between the radially external end of the turnup and a radiallyinternal point F with respect to the end of said turnup, said pointbeing situated on the sidewall and at a distance from said radiallyexternal end by a length greater than 10 mm, and wherein the radiallyexternal end of the turnup is disposed between the rim flange top C anda point D, said points C and D being situated at the surface of thesidewall and disposed on either side of a point E situated on thesidewall corresponding to the nominal section width, said point D beingdisposed at a maximum radial length equal to 85% of the length presentbetween the axial end S of the crown reinforcement and the rim flangetop C.
 2. The tire according to claim 1, wherein the decouplingelastomer composition is present between the radially external end ofsaid turnup and a point G situated radially on the inside with respectto said end and at a distance from said radially external end by alength less than or equal to 10 mm.
 3. The tire according to claim 1,wherein the reinforcers of the carcass ply are set at an angle of lessthan or equal to 85° with respect to the circumferential directionbetween the points C and D.
 4. The tire according to claim 3, whereinthe reinforcers of the carcass ply are set at an angle equal to +75° or−75° with respect to the circumferential direction between the points Cand D.
 5. The tire according to claim 3, wherein the reinforcers of thecarcass ply are set at an angle successively equal to −75°, +75°, +75°starting from the most outward direction to the most inward direction inthe axial direction between the points C and D.
 6. The tire according toclaim 1, wherein the reinforcers of the carcass ply are set at an angleof greater than or equal to 85°, with respect to the circumferentialdirection between the points D and S.
 7. The tire according to claim 1,wherein starting from the point S and in the direction of the axis ZZ′,the reinforcers of the carcass ply are set at an angle equal to 90° withrespect to the circumferential direction.
 8. The tire according to claim1, wherein the reinforcers of the carcass ply are made of a textilematerial chosen from rayon, nylon, polyester, aramid or a mixturethereof.
 9. The tire according to claim 1, wherein between 3 and 8% ofthe reinforcers of the central part are cut.
 10. The tire according toclaim 9, wherein the cut reinforcers of the central part areconsecutive.
 11. The tire according to claim 1, wherein the decouplingelastomer composition has secant modulus at 10% extension of greaterthan or equal to 30 MPa and less than or equal to 60 MPa.
 12. The tireaccording to claim 1, wherein the reinforcers of the carcass ply are setat an angle equal to 90° with respect to the circumferential directionbetween the points D and S.